Chiral materials exhibiting no center of symmetry are isotropic birefringent materials having a "handed" molecular structure. This handedness makes them optically active and capable of rotating a plane of polarized light transmitted through them. Polarizing coatings and filters comprise birefringent materials capable of transforming light into polarized light. Thus, chiral materials may be used as polarizers in the fabrication of plane polarized lenses and polarizing coatings and filters.
Recently, Pelet and Engheta in IEEE Transactions on Antennas and Propagation 38, 90-98 (1990) have suggested the use of optically active materials in guided-wave structures to produce chiral waveguides. A chiral waveguide, also known as a chirowaveguide, comprises a cylindrical waveguide or parallel conducting plates filled with a homogeneous isotropic chiral material. Applications for chiral waveguides include integrated optical devices, telecommunications electronics systems, printed-circuit elements, and optoelectronics devices.
Organic polymers are known to be compatible with semiconductor electronics technology, can withstand high temperatures during processing, and have a large capacity for engineered properties. In addition, it is well-known that high molecular weight polycarbonates are excellent materials for optical applications because of their inherent toughness, durability, resistance to heat and cold, and clarity. The most familiar linear polycarbonates are homopolymers derived from 2,2-bis(4-hydroxyphenyl)propane, commonly known as bisphenol-A (also referred to herein as "BPA"). Polycarbonates derived from BPA are optical quality plastics that can be injection molded to form optical materials such as lenses, substrates for optical storage media including compact disks, and automotive tail lights, for example.
Less familiar polycarbonates are those reported by Wimberger Friedl et al. in U.S. Pat. No. 5,424,389 and European Patent Application 0621297A2 and disclosed by Faler et al. in U.S. Pat. No. 4,950,731. These polycarbonates comprise random copolycarbonates of BPA and 6,6'-dihydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane (also referred to herein as "SBI") which also exhibit the requisite properties necessary for such optical applications. Random copolycarbonates comprising BPA and SBI are also reported by K. C. Stueben in J. Poly. Sci., Part A, 3, 3209-17 (1965). Copending commonly assigned application, U.S. Ser. No. 08/920931, discloses alternating linear polycarbonates derived from spirobiindanols and dihydroxyaromatic compounds. The aforementioned polycarbonates are also transparent and exhibit excellent thermal and mechanical properties.
Poly(aryl)esters, or polyarylates, are high molecular weight aromatic polyesters derived from aromatic dicarboxylic acids and phenols. Polyarylates are known to exhibit mechanical and thermal properties similar to those of polycarbonates. In particular, they are thermally stable at high temperatures, resilient, tough, durable, hydrolytically resistant, transparent, and exhibit excellent processability. The most common polyarylates are those prepared by the reaction of isophthaloyl and terephthaloyl chlorides with BPA.
Brunelle et al. disclose in U.S. Pat. No. Re. 34,431 cyclic polymers prepared from racemic spirobiindane compounds. These cyclic polymers include high molecular weight cyclic spirobiindane polycarbonates and polyesters, which can then be converted to linear polymers.
Polyurethane polymers are high molecular weight thermoplastic polymers useful in a variety of forms, such as fibers, coatings, elastomers, and foams. As coatings, the polyurethanes exhibit excellent hardness, flexibility, abrasion and hydrolytic resistance, and adhesion. In addition, they are tough, durable, and thermally stable at high temperatures. Polyurethanes are often used as wire coatings in electrical applications. The Stueben reference mentioned above discloses polyurethane polymers prepared from racemic SBI.
In general, most applications of synthetic polymers require good thermal stability to withstand high temperature processing (&gt;150.degree. C.), but do not require optical activity. However, for use in the formation of polarizing coatings, lenses, or filters and for utility as chiral waveguides in optoelectronics devices, birefringent materials having polarizing properties must be employed. Due to the low birefringence of the achiral prior art polycarbonate, polyester, and polyurethane polymers mentioned above, they are not useful in such applications.
A need therefore exists for optically active organic polymers that retain the same advantageous properties associated with high molecular weight polycarbonates, polyesters, and polyurethanes. In particular, such chiral polymers should have excellent processability and high molecular weight, and should be durable, tough, thermally stable and water resistant. The novel chiral polycarbonate, polyester, and polyurethane polymers of the present invention meet the above need.